Investigation of R260 Quality Rail Microstructure and Mechanical Properties Combined with Thermite and Flash Butt Welding

Öz

The aim of this study is to examine the microstructure and mechanical properties of thermite and flash butt rail welding methods, which are the two most common methods used in joining rails. The rail used in this study has EN 13674-1 standard, R260 quality, 60E1 profile and 1 m length. The rails with the specified features are combined with termite and flash butt-rail welding methods for the necessary work. Termite rail welding was built in TCDD DATEM and flash butt rail welding was done in TCDD Çankırı Scissor Factory. Residual stress, microstructure, hardness and tensile properties of post-weld thermite and flash butt rail welding, parts taken from rail cork were investigated. According to the residual stress results, the residual stress value of the original unwelded rail was 154 MPa, the residual stress value of the termite rail welding was 172 MPa and the residual stress value of the flash butt rail welding was 160 MPa. According to the microstructure results, when the microstructure of the termite rail welding was examined, it was observed that the structure was ferrite and perlite but not martensite. When the microstructure of the flash butt rail weld was examined, it was observed that the structure was mostly perlitic with ferrite. According to the hardness test results, the hardness values in thermite rail welding were observed as an average of 292 HV1 in the weld center, an average of 310 HV1 between the weld center and ITAB, an average of 308 HV1 in the ITAB, an average of 264 HV1 between the ITAB and the rail metal, and an average of 251 HV1 in the rail metal. The hardness values in the flash butt rail welding were observed as an average of 296 HV1 in the weld center, an average of 298 HV1 between the welding center and ITAB, an average of 292 HV1 in the ITAB, an average of 256 HV1 between the ITAB and the rail metal, and an average of 265 HV1 in the rail metal. According to the tensile test results, the tensile specimen of thermite rail weld broke from the weld center, and the flash butt rail weld specimen broke just after the end of the HAZ. It has been observed that both termite and flash head rail welding material exhibit a ductile behavior. According to the microstructure analyzes of the rupture regions taken from the cross-section, cementite network distribution was observed in most of the microstructures of thermite and flash butt welded rails, and the rupture process was from the dense cementite area that caused brittleness.

Anahtar Kelimeler

• Rail
• thermite welding
• flash butt welding
• microstructure
• mechanical properties

Proje Numarası

KBÜBAP-18-YL-101

Termit ve Yakma Alın Kaynağı ile Birleştirilmiş R260 Kalite Rayın Mikroyapı ve Mekanik Özelliklerinin İncelenmesi

Öz

Bu çalışmanın amacı rayların birleştirilmesinde kullanılan en yaygın iki yöntem olan termit ve yakma alın ray kaynağı yöntemlerinin mikroyapı ve mekanik özelliklerini incelemektir. Bu çalışmada kullanılan ray EN 13674-1 standarda, R260 kaliteye, 60E1 profile ve 1 m uzunluğa sahiptir. Belirtilen özelliklerdeki raylar, gerekli çalışmalar için termit ve yakma alın ray kaynağı yöntemleri ile birleştirilmiştir. Termit ray kaynağı TCDD DATEM’de, yakma alın ray kaynağı ise TCDD Çankırı Makas Fabrikası’nda yaptırılmıştır. Kaynak sonrası termit ve yakma alın kaynaklı rayın, ray mantarından alınan parçaların kalıntı gerilme, mikroyapı, sertlik ve çekme özellikleri incelenmiştir. Kalıntı gerilme sonuçlarına göre, orijinal kaynaksız rayın kalıntı gerilme değeri 154 MPa, termit kaynaklı rayın kalıntı gerilme değeri 172 MPa ve yakma alın kaynaklı rayın kalıntı gerilme değeri ise 160 MPa olarak bulunmuştur. Mikroyapı sonuçlarına göre, termit kaynaklı rayın mikroyapısı incelendiğinde, yapının ferrit ve perlit olup, martenzit olmadığı gözlemlenmiştir. Yakma alın kaynaklı rayın mikroyapısı incelendiğinde, yapının çoğunlukla ferrit ile perlitik olduğu gözlemlenmiştir. Sertlik testi sonuçlarına göre, termit ray kaynağındaki sertlik değerleri kaynak merkezinde ortalama 292 HV1, kaynak merkezi ile ITAB arasında ortalama 310 HV1, ITAB’da ortalama 308 HV1, ITAB ile ray metali arasında ortalama 264 HV1 ve ray metalinde ortalama 251 HV1 olarak gözlemlenmiştir. Yakma alın ray kaynağındaki sertlik değerleri, kaynak merkezinde ortalama 296 HV1, kaynak merkezi ile ITAB arasında ortalama 298 HV1, ITAB’da ortalama 292 HV1, ITAB ile ray metali arasında ortalama 256 HV1 ve ray metalinde ortalama 248 HV1 olarak gözlemlenmiştir. Çekme testi sonuçlarına göre, termit kaynaklı rayın çekme numunesi kaynak merkezinden, yakma alın kaynaklı ray numunesi ise ITAB’ın hemen bitiminden kopmuştur. Hem termit hem de yakma alın kaynaklı ray malzemelerinin sünek bir davranış sergilediği gözlemlenmiştir. Kopma bölgelerinin kesitten alınan mikroyapı analizlerine göre, termit ve yakma alın kaynaklı raylardaki mikroyapıların büyük bir kısmında sementit ağı dağılımı gözlemlenmiş olup, kopma işlemi kırılganlığa neden olan yoğun sementit alanından olmuştur.

Anahtar Kelimeler

• Ray
• termit kaynağı
• yakma alın kaynağı
• mikroyapı
• mekanik özellikler

Destekleyen Kurum

Karabük Üniversitesi

Proje Numarası

KBÜBAP-18-YL-101

Kaynakça

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